Re: CONVERGENCE PROBLEMS WITH CONTROLER (TYPE 2A)

["David Bradley" <bradley@xxxxxxxxxxxxxxx>]

Dear David,
>From - Jan 1965 00:00:00
Received: from brooks.doit.wisc.edu (brooks.doit.wisc.edu [144.92.9.33])          by svrful.ful.ac.be (2.5 Build 2640 (Berkeley 8.8.6)/8.8.4) with ESMTP  id SAA01254; Wed, 05 Sep 2001 18:52:28 +0200
Received: from brooks.doit.wisc.edu (localhost [127.0.0.1]) by brooks.doit.wisc.edu (8.11.1/8.11.1) with SMTP id f85Go2t03502; Wed, 5 Sep 2001 11:50:02 -0500
Received: from mendota.terracom.net (IDENT:root@mendota.terracom.net [208.170.71.129]) by brooks.doit.wisc.edu (8.11.1/8.11.1) with ESMTP id f85Gmjt25716 for <trnsys@relay.doit.wisc.edu>; Wed, 5 Sep 2001 11:48:45 -0500
Received: from dell-700.tess-inc.com (3C2-143.terracom.net [208.170.95.143]) by mendota.terracom.net (8.9.1a/8.9.3) with ESMTP id LAA25158 for <trnsys@relay.doit.wisc.edu>; Wed, 5 Sep 2001 11:48:15 -0500 (CDT)
Message-ID: <4.3.2.7.2.20010905113402.00b4d620@127.0.0.1>
X-Sender: thornton/pop.terracom.net@127.0.0.1
X-Mailer: QUALCOMM Windows Eudora Version 4.3.2
Date: Wed, 05 Sep 2001 11:47:48 -0500
To: <trnsys@relay.doit.wisc.edu>
X-Priority: 3
From: "Jeff Thornton" <thornton@tess-inc.com>
X-MSMail-Priority: Normal
Subject: Re: CONVERGENCE PROBLEMS BECAUSE OF USE OF CONTROLLER (TYPE 2A)
In-Reply-To: <18af613623.1362318af6@teleline.es>
MIME-Version: 1.0
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2600.0000
Content-Type: text/plain;
	charset="iso-8859-1";
	format=flowed
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted: from quoted-printable to 8bit by brooks.doit.wisc.edu id f85Gmjt26234
Reply-To: <trnsys@relay.doit.wisc.edu>
Sender: <owner-trnsys@relay.doit.wisc.edu>
X-Listprocessor-Version: 8.2.06 -- ListProc(tm) by CREN

At 07:01 PM 9/1/01 +0200, you wrote:

>So I have tried to use a controller (TYPE 2A), using as monitoring
>temperature the cold-side outlet temperature and setting 55 as high
>limit cut-out. The upper input temperature is linked to cold-side
>outlet temperature too, and the lower input temperature is always 0. In
>this way, the controller should always shows a 1 as output control,
>except when the temperature to be monitored goes over 55 ºC. However,
>this doesn´t run. I find convergence problems (error 203).

Although your problem seems complicated - its actually a very easy fix to 
get it to work correctly.  Have the high-side inlet temperature to the 
controller set to be a constant - in your case the set-point of 55 C is 
appropriate.  Have the low-side temperature input be connected to the 
temperature input that you do not want to exceed.  Set the high-limit 
cutout to some artificially high value.  Set the upper deadband to 
something reasonable (2 C for example) and the lower deadband to 
0.  Connect the output control signal to the input control signal.